High temperature electronic chip operability depends primarily on chip packaging. Currently, wedge and ball wire bonding techniques are primarily used in prior art devices to interconnect electronic chips and the corresponding package. The biggest limitation associated with this packaging, however, is the failure of metallurgical interconnections between the chip and the corresponding package due to metal incompatibility.
As illustrated in FIG. 1, there is shown a prior art configuration of a chip-package assembly having high temperature operability of up to 200° C. As illustrated, a gold wire interconnects aluminum pads disposed on a chip and gold-plated areas on a corresponding package, thus forming gold-aluminum intermetallic compounds, commonly known as “purple plaque”. These gold-aluminum intermetallic compounds, however, are prone to bond degradation and/or failure at temperatures above 200° C. Such degradation and failure becomes more pronounced with increased temperature, and this interconnection scheme becomes impractical for operation in environments exceeding 225° C. Such characteristics are common between incompatible metals, as incompatible metals are prone to bond degradation and failure at their interfaces.
A number of metallurgical interconnection schemes involving aluminum, indium, gold, silver, platinum, nickel, copper, etc., have been used as alternative interconnect embodiments, however none of these elements provide a clear-cut interconnect solution. The most widely used alternative method utilizes an aluminum wire to interconnect aluminum pads on a chip and gold plated glass/pins on a package. This prior art configuration is illustrated in FIG. 2. In this configuration, however, Kirkendall voids and intermetallic formation remain factors at the aluminum/gold plated pad interface at temperatures exceeding 200° C.
As demonstrated, the presence of aluminum-to-gold interfaces present temperature limitations in prior art configurations. However, separate aluminum-to-aluminum and gold-to-gold interfaces exhibit excellent performance characteristics with no signs of failure at temperatures above 250° C., thus the present invention describes a novel approach to solving the aforementioned interconnection problems by eliminating incompatible metal interfaces of the prior art.